This invention relates generally to a burner and more particularly to a gas mixing line burner.
At the present time, there are three basic types of line burners which are being sold commercially. The first and perhaps oldest type is known as a ribbon burner and is supplied with premixed air and fuel. Approximately sixty percent of the air necessary for combustion is supplied through the burner manifold and ports while the remaining forty percent of the combustion air is picked up from the ambient atmosphere in the vicinity of the burner. The turndown ratio of a burner of this type is in the relatively low order of about three to one. In other words, the heat input at the burner at maximum firing rate is only about three times as great as the heat input when the burner is operated at minimum firing rate. Moreover, a ribbon burner is not useful in airstreams because even the slightest air movement will extinguish the flame. The burner is unable to operate in oxygen deficient atmosphere and thus is not useful in many oven, dryer and furnace applications. The maximum input of such a burner is about 30,000 BTU/HR per lineal ft.
A second type of line burner is a premix burner in which a nearly stoichiometric mixture of air and fuel is supplied to the burner manifold and ports. The burner maintains flame retention by impinging small flame jets off of an ignition retention wall. Usually, the maximum turndown ratio is about eight to one. The minimum input of such a burner is limited because the rate of flame propogation can cause flashback into the manifold. The maximum input of a premix burner is about 400,000 BTU/HR per lineal ft. and is limited by the inability of the burner to maintain flame retention at high mixture pressures and by excessive noise which results from such high pressures. A burner of this type has only limited use in slow moving airstreams and does not lend itself well to high temperature applications.
The third basic type of commercially available burner consists of a fuel manifold or a fuel/air manifold along with a pair of stainless stell mixing plates located on the sides of the manifold. Air is forced through apertures in the mixing plates by a combustion air blower on the burner or is induced to flow through the apertures by air movement in a large duct. While a burner of this type has an excess air turndown ratio which is relatively high, it is incapable of being turned down stoichiometrically. Stated differently, the air and fuel to such a burner cannot be turned down so that only enough oxygen is present for complete combustion of the fuel at all inputs within a wide range of inputs. This type of burner, due to its metallic mixing plates, cannot withstand prolonged exposure to the temperatures normally encountered in furnace applications. In addition, a burner capable of stoichiometric operation is often required. The maximum input of this type of burner is about 1,000,000 BTU/HR per lineal ft.